This invention relates to a method for manufacturing steel bar having intermittent smooth surface segments and patterned relief segments. The steel bar thus manufactured is easily transformed by further processing into mine roof bolts in the manner described below.
The invention according to this application is related to an existing product which is generically referred to as reenforcing bar or "rebar." Therefore, the term "rebar" will be used in this application to mean a substantially round in cross-section steel bar having a raised pattern integrally formed on its surface. Rebar is typically used in concrete construction to reinforce a concrete structure by forming a web which is completely encased in concrete. The raised pattern on the surface of the bar forms gripping surfaces around which the concrete hardens. Once the concrete hardens, shifting is prevented by the outwardly protruding pattern on the bar.
Rebar bar has also been used in the mining industry. In many types of underground mines, safety regulations and good mining practice require that a suspended ceiling be bolted into place over the roof of the mine shaft. This is accomplished by drilling a series of spaced-apart, vertically extended holes in a mine shaft ceiling. An epoxy material is placed in each hole and then a length of steel reinforcing bar is inserted into the hole. The epoxy hardens around the rebar and holds it in place. Typically, 6 to 12 inches of the rebar extends downwardly from the plane of the ceiling and is threaded to receive a bolt. A ceiling panel having suitably spaced holes is placed on the ceiling with the rebar extending downwardly through the holes. Then, bolts are threaded onto the bars and the ceiling is suspended in place. Heretofore, the type of rebar used has been a rebar which has a pattern extending continuously along its entire length. Therefore, the bar would be cut to an appropriate length to serve as a mine roof bolt and then the raised pattern on several inches of one end of the bar would be removed either be swaging or grinding. Then, threads would be rolled or cut onto that end of the bar to recieive the nut. This practice has presented a number of problems.
First, the pattern traditionally found a rebar--usually a diamond-shaped pattern, is not ideal for use as a mine roof bolt. Furthermore, it is expensive and time consuming to individually swage or grind off the pattern on each of many hundreds or thousands of bolts after they are cut and before they are threaded.
These and other problems are resolved by manufacturing a metal, preferably steel, bar with intermittent smooth surface segments and patterned relief segments, as described below. The invention disclosed herein permits a length of bar to be cut to the desired length for use as a mine roof bolt and immediately threaded to receive a nut without intermediate processing.